Permafrost Evolution in Subarctic West Siberia Since Marine Isotope Stage 3 Evidenced by Relics of Cryogenic–Cryopedogenic Interaction

A novel glacier‐free scenario of the Late Pleistocene environmental change in the North‐Western (NW) Siberia stimulated the search for the legacies of the permafrost evolution arising from the interaction of cryogenic and cryopedogenic phenomena. In this paper we present the issue of such investigation through the development of a specific Taz‐Nadym cryopedogenic horizon formed under permafrost conditions during MIS2—Sartanian cryochron. It includes the formation of enough large polygonal ice wedge (PIW) pseudomorphs, whereas the original PIWs grew epigenetically throughout the major part of MIS2, penetrating into the alluvial sandy deposits of the terrace bodies accumulated in MIS3. PIWs began to melt during the warming at the end of the MIS2, Sartanian cryochron, and the pedosediments developed under permafrost conditions have derived from the soil mantle adjacent to the PIWs and filled the space left by ice. We discriminate the cryogenic and pedogenic blocks of paleocryological ‘memory’ of this horizon responsible for different time intervals. The cryogenic record includes different characteristics yielded by PIW development (geometry of polygons, size and shape of individual wedges, deformation of host sediments) and is indicative of the climatic and permafrost conditions. Paleosol cryogenic memory is based on the morphological features of pedosediments which show strong gleization indicative of the cryohydromorphic type of pedogenesis. Important information was also obtained from the fragments of the paleosol humus providing in the filling of PIW pseudomorphs organic matter for radiocarbon dating and analysis of its composition (relative amount of humic and fulvic acids).